Apparatus for the continuous extraction of electroslag remelted metals

ABSTRACT

An electroslag melting (e.g. remelting) of metal, under a slag or fused-flux layer, is carried out in a crucible provided with a discharge neck which is received with clearance in a removable, replaceable and interchangeable continuous-ingot mold. The liquid/solid metal interface is maintained within the mold which has a liquid-free surface exposed to reducing or nonoxidizing gas pressure maintained to balance the hydrostatic pressure of the metal bath and flux layer in the melting chamber. As a consequence, the rate of flow of the metal from the melting crucible to the ingot mold is automatically controlled to equal the rate at which the ingot is withdrawn.

United States Patent [191 Metz [ APPARATUS FOR THE CONTINUOUS EXTRACTIONOF ELECTROSLAG REMELTED METALS [75] Inventor: Paul Metz, Emile Metz,

Luxembourg [73] Assignee: Acieries Reunies de Burbach-Eich-DudelangeS.A., Luxembourg, Luxembourg [22] Filed: Apr. 14, 1971 [21] Appl. No.:133,993

[30] Foreign Application Priority Data Apr. 16, 1970 Luxembourg 60743[52] US. Cl 164/156, 164/252, 164/281, 164/337 [51] Int. Cl B22d 17/32,B22d 27/02 [58] Field of Search... 164/113, 119, 154, 155, 156, 164/284,306, 335, 337, 281, 82, 52, 254-259 [56] References Cited UNITED STATESPATENTS 2,825,104 3/1958 Jones 164/83 X 3,234,608 2/1966 Peras 164/52Jan. 29, 1974 3,587,718 6/1971 Hopkins 164/82 X 3,650,311 3/1972Fritsche 164/82 X 2,445,670 7/1948 Hopkins r 154/252 3,608,616 9/1971Schneider 164/154 FOREIGN PATENTS OR APPLICATIONS 444,390 2/1968Switzerland 164/337 Primary Examiner-J. Spencer Overholser AssistantExaminer-John E. Roethel Attorney, Agent, or Firm-Karl F. Ross [5 7ABSTRACT An electroslag melting (e.g. remelting) of metal, under a slagor fused-flux layer, is carried out in a crucible provided with adischarge neck which is received with clearance in a removable,replaceable and inter changeable continuous-ingot mold. The liquid/solidmetal interface is maintained within the mold which has a liquid-freesurface exposed to reducing or nonoxidizing gas pressure maintained tobalance the hydrostatic pressure of the metal bath and flux layer in themelting chamber. As a consequence, the rate of flow of the metal fromthe melting crucible t0 the ingot mold is automatically controlled toequal the rate at which the ingot is withdrawn.

10 Claims, 3 Drawing Figures PATENTED N 29 I97 IVONOXID;

GAS

Paul Mefz INVENTOR.

KIM. {R958 Attorney APPARATUS FOR THE CONTINUOUS EXTRACTION OFELECTROSLAG REMELTED METALS FIELD OF THE INVENTION My present inventionrelates to an apparatus for the continuous production of elongated metalbodies, especially ingots, bars, billets and blooms of electricallyremelted metals; more particularly, the invention relates to anelectroslag remelting apparatus in which a continuous withdrawal ofmetal is effected.

BACKGROUND OF THE INVENTION Electrical methods for remelting metals,especially electroslag remelting, refining or melting, generally makeuse of a fused layer of nonmetallic material, generally referred to asflux, which overlies the metallic bath and serves as an intermediarybetween the electrode and the metal. The slag which may overlie themetal bath in a layer continuously interacting with the metal andserving as a medium through which electric current is caused to flow toprovide the resistive heating necessary to melt the metal or maintainthe metal in a molten state. For convenience, such systems, using fluxor slag as an electrode-submerging medium, will be referred tohereinafter as electroslag remelting or electroslag melting.

In general, two or more flux-submerged electrodes are spaced apart inthe vessel and terminate just above the molten metal layer therein. Anelectric current or discharge may pass between the electrodes, throughthe molten metal, to melt the electrodes and/or additional metal andproduce the physical, mechanical and chemical interaction of melting,fusing and purification of the melt in interaction of the hot slag orflux with the metal. The metal derive from the electrodes or may beprovided in the form of coherent units, e.g. pieces of scrap or pellets,granules or briquettes of metallic iron or, as metal powders, and in anyform available. In principal, the slag or flux layer of electroslagremelting and melting processes not only provides a medium capable ofdischarge or current flow, but also of chemically reacting with moltenmetal for purification and providing a blanket which excludes air orother detrimentally reactive substances from the molten metal.

It has also been proposed to provide continuous casting systems in whichthe molten metal is permitted to flow into a tubular ingot mold and tosolidify therein, the ingot being continuously withdrawn from the mold.

Neither method has been fully successful heretofore because of thelimited production rate, the fact that control of the flow of the liquidmetal into the ingot mold is difficult, and because complicatedapparatus is required when, for example, different shapes are to becast. The difficulty is compounded by the fact that it may be desirableto continuously cast different flow cross-sections or cross-sectionalconfigurations and hence requiring different rates of flow of the moltenmetal. Under these circumstances, conventional flowregulation systemshave proved to be inadequate.

OBJECTS OF THE INVENTION It is the general object of the presentinvention to provide an improved apparatus for the continuous remeltingof metal and the formation of a continuous shaped product which is ofimproved efficiency and affords simplicity of control and variability ofthe product. Another object of the invention is to provide an apparatusfor continuously melting and resolidifying metal whereby theaforementioned disadvantages can be avoided.

Still another object of the invention is to provide an apparatus for thecontinuous withdrawal of molten metal from an electroslag remeltingcrucible in which the control of the flow rate is substantiallyautomatic and can compensate for variations in the flow crosssection ofthe ingot mold and other parameters.

Yet another object of the invention is the provision of an apparatus forthe continuous remelting and resolidification of metal to produce avariety of shapes at higher rates than have been realized heretoforewith less difficulty in controlling the system and with increasedefficiency.

SUMMARY OF THE INVENTION I have now found that these objects can beattained in a remelting system using electroslag principles where theremelting crucible and the solidification mold com municate with oneanother but are functionally independent and are so constructed andarranged that the liquid/solid interface is maintained in the ingot moldand the liquid forms of meniscus therein which is exposed tononoxidizing or reducing gas pressure. The gas pressure, according tothis invention is arranged to substantially balance the hydrostatic headattributable to the metal bath and the slag or flux layer overlying samein the melting crucible. In other words the rate of flow of the moltenmetal is controlled by the withdrawal of the ingot from the mold suchthat the meniscus remains at a substantially constant location duringthe casting and solidification process as a result of the controlledpressure applied to the free surface of the melt within the ingot mold.

According to the present invention, therefore, the remelting crucibleand the mold are functionally independent and the latter is replaceable,interchangeable and exchangeable with other molds of differentconfigurations and flow cross-sections. According to an essentialfeature of the invention, the remelted metal is drawn from the baththereof below the slag or flux layer so as to maintain a free surface ofthe melt, e.g. the metal or a slag layer, which is under a nonoxidizingor reducing gas pressure equal to the pressure exerted by the column ofmetal and slag above the predetermined meniscus level. By separating theremelting and solidification operations, it has become possible to allowa single remelting crucible to feed a plurality of solidification moldseach associated with the remelting crucible in the manner alreadydescribed to provide the necessary free space and control the gaspressure. It has also been found that these techniques are especiallysuitable for the production of bars or continuous ingots of smallcross-section at maximum output without any of the disadvantagesmentioned earlier of continuous casting systems.

The electroslag process may use consumable or nonconsumable electrodes,in accordance with conventional techniques, and, according to theinvention,

melting crucible contains only the flux or slag bath in which the, oreach, electrode is immersed as a layer above the layer of molten metal,the latter being of a depth only sufficient to allow decantation ofimpurities. It will be appreciated that within the crucible theinteraction of the flux or slag with the metal, and of added quantitiesof metal with previously smelted metal, etc., leads to a separation ofimpurities from the melt. These impurities rise into the slag or fluxlayer and, for the purposes of the present invention, it has been foundto be desirable to maintain a depth of molten metal with the crucibleonly sufficient to allow a decantation of impurities into the slaglayer.

The crucible is provided with one or more discharge tubes which may bepreferably of large flow crosssection, the flow cross-section beingimmaterial to the cross-sections of the ingot molds with which thedischarge tubes or necks register. Each tube or neck is preferablyreceived with clearance in the respective mold so that a liquid meniscusis exposed to the pressurizable chamber above the ingot mold whosenonoxidizing or reducing pressure is controlled in accordance with theprinciples advanced earlier. The neck or tube of the crucible may beimmersed in the liquid within the ingot mold or may be spaced slightlyabove the meniscus by several millimeters. As indicated, the ingot moldsmay have cross-sections and configurations which are independent of theflow cross-section of the discharge tubes of the crucible. In fact, thedimensions and cross-sections of the ingot molds need correspond only tothe profile of the metal bodies to be produced and their dimensions.Above the, or each, ingot mold I provide a respective pressure chamberin which the nonoxidizoning or reducing gas pressure is regulatedautomatically to balance the hydrostatic head or equivalent pressure ofthe metal within the crucible, thereby controlling automatically theoutflow of liquid metal into the mold as a function of the speed atwhich the ingot is withdrawn so that the meniscus of the metal or slaglayer overlying same in the lingot mold remains at a substantiallyconstant location.

It has been found to be advantageous, as far as apparatus aspects of thepresent invention are concerned, to provide means for supplying gasunder pressure to the gas chamber above the ingot mold and to connectthis chamber with a valve having a back pressure determined by theliquid head as noted earlier. Furthermore, heat losses from theotherwise cool ingot mold may be prevented by providing a thermallyinsulating zone in the region of the meniscus with or without heatingelements and it has also been found to be desirable to provide suchheating means in the discharge tube or neck of the crucible. Finally,pressure-controlled cut-off means may be provided at the, or each, tubeor neck to terminate the flow of molten metal into the ingot mold or topermit the flow to begin again; such shutter means need not, however,control the rate of flow of the liquid metal to the ingot mold, sincethis control is provided automatically as indicated above.

DESCRIPTION OF THE DRAWING The above and other objects, features andadvantages of the present invention will become more readily apparentfrom the following description, reference being made to the accompanyingdrawing in which:

FIG. I is a vertical cross-sectional view partly in diagrammatic form,of an apparatus illustrating the present invention;

FIG. 2 is a diagrammatic detail view showing an arrangement of thedischarge tubes and the meniscus; and

FIG. 3 is a view similar to FIG. 2 of another embodiment.

SPECIFIC DESCRIPTION In FIG. 1 of the drawing I have shown a system,according to the present invention, which comprises a ceramic crucible 1for the remelting of metal under a slag or flux layer 2 to form amoltenmetal bath 3 in accordance wifli conventional practices. The metalwithin the bath is, of course, liquid in its entirety and melting iscarried out in accordance with'electroslag principles with the aid ofelectrodes 4 immersed in the flux/slag layer and connected, for example,to a three-phase source which passes electric heating current betweenthe pairs of the electrodes in turn. In principle, the heat loss fromthe crucible may be reduced by forming a crucible of a layer ofheat-insulating ceramic l internally of a metal shell which has beenshown diagrammatically at 1a in FIG. 1. Furthermore, electric heatingelements as illustrated at 11) may be provided in the wall or as awrapping 1c therearound.

The crucible l is dimensioned to have the necessary horizontal sectionto accommodate the electrodes used. The greater the capacity, of course,the larger will be the number or the cross-section of electrodes spacedapart in the flux/slag layer. However, the depth D of the metal bath ismade as small as possible consistent with the height necessary to allowdecantation of the impurities from the molten metal. The free largehorizontal section/vertical height ratio characterizing the shallowbathcrucible provides a maximum interfacial area at M for heat exchange andchemical reaction between the flux/slag layer and the metal bath.

The crucible 1 is provided with a bottom 1e which converges slightlydownwardly to a plurality of discharge tubes or necks 7, only one ofwhich has been shown in the drawing. However, each of the dischargetubes may be constructed similarly and may be provided with respectiveingot molds as will be apparent hereinafter.

The bottom orifice 7a of the crucible may equal the discharge orifice 7bof the neck in diameter and configuration so that the internal basis ofthe neck is generally cylindrical. The tube 7, moreover, is providedwith a closure device represented generally at 5 or 6. The closuredevice comprises a slide 5 provided with an aperture 5a which registerswith the passage 7c in the open position of the closure device. When,however, the slide 5 is shifted to the right or left, by a cylinder 6pneumatically controlled by the pressure in chamber 10 (describedhereinafter) or by pressure from an auixilary source represented at Sand delivered through the valve V, the flow of liquid can be terminated.The valve V may be automatically or manually operated to start the flowof molten metal or to stop it. Similarly, the control device 6 may beregulated by the pressure in chamber 10 so that, should the meniscus inthe mold suddenly rise or fall beyond the predetermined limit the flowof metal will be cut off. In any event, the shutter 5 is not used tocontrol the rate of flow of the metal.

Each tube 7 is received within an ingot mold 8 which may be of theliquid-cooled type. In this case, the mold walls are provided withcooling ducts which are supplied with cooling water by a feeding tube 8athe depleted coolant being led away at 8b. The ingot mold 8 is of thetype used for the continuous casting of circular cross-section, squarecross-section or flat (rectangular) cross-section in conventionalcontinuous casting systems. At the upper ends of the ingot molds 8, ahermetic seal is formed with a housing a defining a chamber 10 which isalso sealed against the floor of the crucible 1. The orifice 7b of thetube 7 may lie some what above the meniscus M of liquid metal formed inthe ingot mold 8 as illustrated in FIG. 3, for example, in which adistance D of several millimeters is provided between the meniscus leveland the discharge end of the tube 7. However, the tube 7 may also beimmersed to a depth of several millimeters within the molten metal asillustrated in FIG. 2. It should be understood that the term moltenmetal" as here used to describe the liquid forming the meniscus isintended to include also any slag layer that may form above the metalmelt solidifying within the ingot mold. In practice, a steadystate iscreated in which the gas pressure P, of chamber 10, exerted downwardlyupon the liquid L above the solidifying interface in the ingot mold,balances the hydrostatic head H of the flux/slag layer 2 and the melt 3thereabove. The meniscus thus lies at a constant level and the flow rateat which the metal L solidifies within the ingot mold.

Where the tube 7 terminates above the meniscus M, one chooses the levelM of the liquid in the ingot mold such that the continuous stream ofliquid metal pours in a quiescent manner without splashing orturbulance.

In each case, a meniscus of the metal in ingot mold 8 is controlled bymaintaining the gas pressure/hydrostatic pressure balance mentionedearlier. The upper portion of the metal in the ingot mold remainspermanently in a liquid state and where the flow rate of the metal isrelatively low, in a case of small-cross section cast body, thesupernatant slag layer S prevents premature coolant. In addition, it ispossible to reduce the heat loss in the area of the meniscus asrepresented at 9 by providing the wall of this part of the ingot of theingot mold of a thermally insulating material or, alternatively,incorporating heating elements 9a of the resistive-heating type therein.To prevent crust formation within the tube 7 or in contact therewith, e.g. where the slag layer may contact the tube, the latter may be providedof thermally insulating material or can be formed with resistive-heatingelements as shown at 11d.

The flow cross-section of discharge tube 7, which is integral with thecrucible 1, may be relatively large and is, in any event, independent ofthe flow velocity of the liquid metal. Thus tube merely establishesintercommunication between the crucible 1 and the ingot mold 8 and doesnot enter into the control of the volume of metal which is cast withinthe ingot mold. The flow of metal into each ingot mold 8 is controlledautomatically in accordance with the resolidification rate of the metalwithin the ingot mold and hence the rate at which the ingot I iswithdrawn by the feed rollers R. Since the speed of resolidification canbe easily controlled, 1 prefer to maintain the ingot formationsubstantially constant and permit the liquid feed rate to adjust itselfaccordingly.

As illustrated in FIG. 1, the ingot mold 8 is a unit independent of themelting crucible 1 but hermetically sealed to the latter. Thus it ispossible to change the ingot molds 8 for others of different profileswithout making any material change in the crucible structure. In fact,the shutter 5 may simply be closed off and another ingot mold attachedto the discharge tube 6 of the crucible. Regardless of the cross-sectionof the ingot mold, therefore, the ingot will be formed at a ratecontrolled by the pressure relationship discussed above and this may beestablished to avoid vortex formation within the crucible 1. Since theingot mold 8 is open at both ends and the discharge tube 7 extendsfreely into the upper end of the ingot mold without engaging the wallsthereof, there is formed a free surface of the metal or of a slag layerin the annular space around the tube 7 and within the ingot mold 8. Thisfree surface receives a gas pressure equal to the effective pressure orhead of the column of liquid metal and slag overlying the meniscus M.Should the head increase, I provide means for increasing the counterbalancing pressure 10 as will be apparent hereinafter.

A duct 11 connected to a source of gas (e.g. nitrogen, hydrogen, carbonmonoxide, methane) under pressure via a valve 11a, opens into thechamber 10a to establish the gas cushion 10 which bears downwardly uponthe free surface of the metal or slag within the ingot mold 8. The space10 is hermetically sealed against the ambient atmosphere by the ingotmold 8 and the crucible l as illustrated in FIG. 1. Sealed joints, notillustrated may be provided in the regions in which the housing 10abears against the crucible and ingot mold. Alternatively, I may providea cover upon the ingot mold 8 which sealingly engages the spigot formedby the tube 7. As long as the liquid metal solidifies at the rate theliquid is supplied the pressure at the free surface of the metal and theposition of the meniscus M will remain constant and independent of thequantity of metal flowing into the ingot mold 8. The ingot may passthrough the latter solely as a result of its weight or by the combinedeffect of its weight and the engagement of the ingot by the rollers R.

To permit the pressure in chamber 10 to equal the head of metal and,therefore, compensate any changes in the head resulting from increase inthe level ofthe metal bath and the overlying flux/slag layer within thecrucible, I provide a branch 12 of conduit 11 which opens into thecrucible at a perforated ceramic plug 13. The pressure in chamber 10 isthus held at a level which is equal to the head if the resistance offlow of the gas through the plug 13 is adjusted with respect to thedifference in heights between the plug 13 and the walls of tube 7. Henceany increase in pressure within chamber 10 beyond that required toplunge the head results in j a bleeding of gas from the plug 13. On theother hand,

the reduction of the level in the crucible 1 also causes an increasedflow of gas from plug 13 and branch 12. The pressure supplied at duct 11may be adjusted to maintain a slight flow continuously from plug 13 sothat any increased height of the bath will result in a proportionalincrease in the pressure within chamber 10. By adjustment of thepressure balance, moreover, it is possible to establish the meniscus atany location within the ingot mold 8 as may be desired. In addition, Imay provide means represented at 2a to sense the level of liquid withinthe crucible I and control the valve 11a for independent regulation ofpressure. Furthermore,

the valve V connects the actuator 6 with the chamber I for automaticcutol'iol the How of liquid should the meniscus level rise suddenly as aresult of a pressure drop in chamber 10 or a related danger condition inthe crucible. Another sensor 80 can be provided for the valve lla if itis desired to maintain the meniscus at a fixed location under allcircumstances.

By maintaining permanently a slight excess pressure in the gas in line11 so that there is a tendency for the gas to vent from the porous plug13, it is possible to balance any tendency of the meniscus to rise orfall as indi' cated earlier. The invention has been described as it isapplicable to an ESR technique for the electroslag remelting of metalusing consumable electrodes under a flux/slag submerging layer. Theprocess may be equally applicable nonconsumable electrodes and/or toelectroslag melting (ESM) in which raw material is iron powder orsponge-iron powder. Furthermore, the system has been found to be mosteffective in the production of elongated bodies of smallcross-sectionwhether square, rectangular or circular and permits progressivesolidification independent of melting.

The improvement described and illustrated is believed to admit of manymodifications within the ability of persons skilled in the art, all suchmodifications being considered within the spirit and scope of theinvention except as limited by the appended claims.

I claim;

1. An apparatus for producing elongated metal bodies, comprising anelectroslag melting crucible adapted to receive a bath of metal overlainby a flux- /slag layer, said crucible being at least one downwardlyextending discharge tube; a replacable ingot mold open at itsextremities and surrounding said tube with clearance while communicatingwith said tube to receive a stream of molten metal therefrom and form acontinuously solidifying ingot from said metal whereby the liquid metalof said stream forms a meniscus within said ingot mold directly adjacentthe lower end of said discharge tube; means forming a gas pressurechamber above said meniscus for applying to the liquid metal in saidingot mold and emerging from said tube a gas pressure approximatelybalancing the liquid head of said bath and said layer above saidmeniscus whereby the liquid metal enters said ingot mold at a rateautomatically adjusted to the rate at which said ingot is formed; andsensing means responsible to the position of said meniscus forcontrolling said gas pressure to maintain said meniscus adjacent saidend to prevent free fall of liquid metal from said tube.

2. An apparatus for producing elongated metal bodies comprising;

an electroslag melting crucible adapted to receive a bath of metaloverlain by a flux/slag layer, said cruciblc having at least onedownwardly extending discharge tube;

a replaceable ingot mold open at its extremities and surrounding saidtube with clearance while communicating with said tube to receive astream of molten metal therefrom and form a continuously solidifyingingot from said metal whereby the liquid metal of said stream forms ameniscus within said ingot mold;

means forming a gas pressure chamber above said meniscus for applying tothe liquid metal in said ingot mold and emerging from said tube a gaspressure approximately balancing the liquid head of said bath and saidlayer above said meniscus whereby the liquid metal enters said ingotmold at a rate automatically adjusted to the rate at which said ingot isformed;

conduit means supplying a nonoxidizing gas under pressure to saidchamber; and

means responsive to the level of said layer and said bath in saidcrucible for controlling the pressure in said chamber,

the last mentioned means including a branch of said conduit meanscommunicating with said crucible below the level of the bath therein,and a porous plug at said branch.

3. The apparatus defined in claim 2 wherein said ingot mold is formed atleast in the region of said meniscus with theremally insulating walls.

4. The apparatus defined in claim 2, further comprising means forheating the walls of said ingot mold at least in the region of saidmeniscus.

5. The apparatus defined in claim 2, further comprising means forcooling at least the portion of said ingot mold downstream of saidmeniscus in the direction of movement of said ingot through said ingotmold.

6. The apparatus defined in claim 2, further comprising means responsiveto the position of said meniscus for controlling the pressure in saidchamber.

7. The apparatus defined in claim 2, wherein said tube is composed atleast in part of thermally insulating material.

8. The apparatus defined in claim 2, further comprising means forheating said tube.

9. The apparatus defined in claim 2, further comprising shutter meansfor closing said tube upon the level of said meniscus varying beyond apredetermined point. I

10. The apparatus defined in claim 2, further comprising shutter meansresponsive to the pressure in said chamber for blocking said tube upon avariation in pressure therein beyond a predetermined level.

1. An apparatus for producing elongated metal bodies, comprising anelectroslag melting crucible adapted to receive a bath of metal overlainby a flux/slag layer, said crucible being at least one downwardlyextending discharge tube; a replacable ingot mold open at itsextremities and surrounding said tube with clearance while communicatingwith said tube to receive a stream of molten metal therefrom and form acontinuously solidifying ingot from said metal whereby the liquid metalof said stream forms a meniscus within said ingot mold directly adjacentthe lower end of said discharge tuBe; means forming a gas pressurechamber above said meniscus for applying to the liquid metal in saidingot mold and emerging from said tube a gas pressure approximatelybalancing the liquid head of said bath and said layer above saidmeniscus whereby the liquid metal enters said ingot mold at a rateautomatically adjusted to the rate at which said ingot is formed; andsensing means responsible to the position of said meniscus forcontrolling said gas pressure to maintain said meniscus adjacent saidend to prevent free fall of liquid metal from said tube.
 2. An apparatusfor producing elongated metal bodies comprising; an electroslag meltingcrucible adapted to receive a bath of metal overlain by a flux/slaglayer, said crucible having at least one downwardly extending dischargetube; a replaceable ingot mold open at its extremities and surroundingsaid tube with clearance while communicating with said tube to receive astream of molten metal therefrom and form a continuously solidifyingingot from said metal whereby the liquid metal of said stream forms ameniscus within said ingot mold; means forming a gas pressure chamberabove said meniscus for applying to the liquid metal in said ingot moldand emerging from said tube a gas pressure approximately balancing theliquid head of said bath and said layer above said meniscus whereby theliquid metal enters said ingot mold at a rate automatically adjusted tothe rate at which said ingot is formed; conduit means supplying anonoxidizing gas under pressure to said chamber; and means responsive tothe level of said layer and said bath in said crucible for controllingthe pressure in said chamber, the last mentioned means including abranch of said conduit means communicating with said crucible below thelevel of the bath therein, and a porous plug at said branch.
 3. Theapparatus defined in claim 2 wherein said ingot mold is formed at leastin the region of said meniscus with theremally insulating walls.
 4. Theapparatus defined in claim 2, further comprising means for heating thewalls of said ingot mold at least in the region of said meniscus.
 5. Theapparatus defined in claim 2, further comprising means for cooling atleast the portion of said ingot mold downstream of said meniscus in thedirection of movement of said ingot through said ingot mold.
 6. Theapparatus defined in claim 2, further comprising means responsive to theposition of said meniscus for controlling the pressure in said chamber.7. The apparatus defined in claim 2, wherein said tube is composed atleast in part of thermally insulating material.
 8. The apparatus definedin claim 2, further comprising means for heating said tube.
 9. Theapparatus defined in claim 2, further comprising shutter means forclosing said tube upon the level of said meniscus varying beyond apredetermined point.
 10. The apparatus defined in claim 2, furthercomprising shutter means responsive to the pressure in said chamber forblocking said tube upon a variation in pressure therein beyond apredetermined level.